The present invention generally relates to cargo handling systems for narrow body freighter aircraft. More particularly, the invention relates to a caster roller cargo handling system for a narrow body freighter aircraft.
In the aviation industry, aircraft have been designed to serve a wide variety of purposes. For example, modern-day airplanes are used for general aviation, passenger transport, and freighter transport purposes. It is typical for freighter aircraft to vary in size from wide body to narrow body depending on the desired cargo payload. For example, wide body freighters such as the B747 are designed to handle payloads on the order of 200,000 pounds, whereas narrow body freighters are designed to carry cargo payloads on the order of 50,000 pounds. Recently, passenger planes such as the Boeing 757-200 have been modified to meet narrow body freighter purposes.
In all freighter applications it is desirable to maximize the volume of the cargo area. This desire has directed attention to cargo handling system design considerations as well as body design considerations. It is therefore particularly desirable to provide a cargo handling system for a narrow body freighter which meets or exceeds volume requirements for industry standard cargo as well as unique cargo.
Typical cargo handling systems provide a mechanism for loading and unloading cargo containers from decks of the freighter. The cargo containers are loaded on pallets which are moved across the deck on ball mats disposed throughout the deck surface. In order to maximize volume (as well as to ensure proper operation), freighters of all size normally specify a roller plane height with respect to the deck surface. For example, narrow body freighters most commonly have a standard roller plane height of 1.25 inches (3.175 centimeters), whereas wide body freighters most commonly have a specified roller plane height of 1.75 inches (4.445 centimeters). However, it possible to incorporate the roller plane height desired on most freighter aircraft whether the aircraft is a narrow or a wide body since some aircraft have 2.00 inch systems (5.080 centimeters).
While caster rollers have been used for wide body freighter cargo handling systems, conventional designs have not been scalable to the lower roller plane height standard for narrow body freighters. This problem is largely due to the complicated nature of the bearing designs for conventional caster rollers. For example, the conventional caster roller has a roller bearing assembly for contacting the cargo pallet and a thrust bearing assembly which aligns the roller bearing assembly with the axis of motion. The roller bearing assembly has typically employed separate roller and bearing components, causing the overall outside diameter to be too large for narrow body freighter purposes. Furthermore, the thrust bearing assembly generally has a feed-through opening for insertion of individual bearings which adds to assembly costs, reduces durability, and increases part costs.
The inability to use conventional caster rollers for narrow body freighter applications has therefore led to the widespread use of ball mats. Ball mats have a spherical roller instead of a cylindrical roller as in the case of caster rollers. The spherical design creates a point load at the point of contact with the pallet. The point load forces are much higher than the line load forces which would be created with a cylindrical roller. Over time, the point load causes pallets to curl up, which is sometimes referred to as xe2x80x9ccold workingxe2x80x9d. Cold working is detrimental to pallets and is extremely undesirable. The creation of a point load also requires the use of a larger number of ball rollers to sufficiently distribute the weight of the pallet and cargo container.
Another shortcoming of ball mats is the increased problem with xe2x80x9cFODxe2x80x9d (foreign object damage). FOD occurs when particles of dust, grease, oil, moisture, etc. penetrate the area between the housing of the ball roller and the ball. FOD substantially reduces the durability of ball mats and ultimately leads to increased warranty claims. It is therefore desirable to provide a cargo handling system which can avoid the problems associated with ball mats, yet still meet the volume requirements of narrow body freighters.
In accordance with the present invention, a cargo system for a narrow body freighter aircraft includes a horizontal panel, a plurality of caster rollers, and an attachment system. The horizontal panel is disposed along a deck surface of the aircraft, and the plurality of caster rollers movably supports a load within the aircraft. Each caster roller has a plurality of roller bearings for providing horizontal movement to the load along an axis of motion. The attachment system couples the caster rollers to the horizontal panel. Thus, the aforementioned problems associated with ball mats can be avoided.
Further in accordance with the present invention, a caster roller for a freighter aircraft cargo handling system includes a roller bearing assembly having a plurality of roller bearings providing horizontal movement to a load along an access of motion. A thrust bearing assembly having a plurality of radially positioned needle bearings aligns the roller bearing assembly with the axis of motion. The caster roller further includes a housing having internal surfaces defining a drop-in channel, and a roller bearing support structure. The drop-in channel contains the thrust bearing assembly, and the roller bearing support structure suspends the roller bearing assembly at a predetermined roller plane height.
The present invention also provides a method for supporting cargo within an aircraft. The method includes the step of using at least one roller bearing to support the cargo thereon. The roller bearing is disposed for rotational movement relative to a support structure such that the roller bearing is disposed at a predetermined height above the support structure. The support structure is supported on a plurality of radially positioned needle bearings to enable the support structure to rotate about an axis normal to a rotational axis of the roller bearing. A ring member is used to support the radially positioned needle bearings, and portions of the ring member are secured to a floor support panel such that the needle roller protrudes outwardly of an outer surface of the support panel.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute part of this specification. The drawings illustrate various features and embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.